This invention relates generally to offshore drilling of wells using floating and non-floating platforms.
A floating platform may be moved to a position over a potential well location. The well may be drilled and may be coupled to the rig by a marine riser. Conventionally, there is a substantial distance between the floating platform and the seabed surface. For example, this distance may be several thousand feet. As a result, it is necessary to lower various drill strings, casings, and risers from the surface to the seabed floor.
The cost associated with drilling wells with offshore floating platforms may be substantial. For example, rental rates for offshore mobile platforms may run in the range of $300,000.00 a day. Significant time may be spent running various equipment from the rig down to the subsea floor. This time may result in a substantial portion of the cost.
Often, it is desirable to drill one well, pick up, and move to another location. The need to connect to a well from the surface involves substantial expenditure of time and, therefore, expense.
To address these problems, so-called dual activity rigs have been proposed. In a dual activity rig there may be two derricks, including a main derrick, used for running and hanging off the blowout preventer, and an auxiliary derrick, used to drill the top hole and run surface casing. A blowout preventer riser may be hung off from the rig while the drill string is operating to form the hole.
Dual operations may save time from the time a rig arrives on location to the landing of the blowout preventer. This is because the riser and the blowout preventer can be made up and run off line.
Thus, there is a need for still better ways to save time during offshore floating platform drilling activities.